Particulate filters may be included in engine exhaust systems to retain particles generated during fuel combustion. As engine exhaust flows through a particulate filter, particles such as soot accumulate in the filter, thereby reducing undesirable exhaust emissions. Because such filters become overloaded with exhaust particles over time, they must be regenerated periodically. Particulate filter regeneration may involve heating the filter to such an extent that the loaded particles may “burn off” or combust. In addition to reducing the particle loading so that additional particles may be retained, particulate filter regeneration helps to ensure a controlled level of exhaust-gas counter-pressure (i.e., pressure exerted on the flow of exhaust by the particulate filter, which may adversely affect engine performance).
However, regeneration alone may not address all of the issues associated with overloading of particulate filters. For example, in the case of high soot loading, the exothermic heat generated during spontaneous soot combustion may damage parts of the exhaust system, and the heat associated with filter regeneration may cause further soot combustion and thus further damage to the exhaust system.
Further, the heat of the regeneration process may be hazardous in some conditions. For example, if a vehicle's engine is shut down during particulate filter regeneration and the vehicle parked in an area with tall grass or other obstructions near the tail pipe, the combination of the heat of regeneration and ignitable materials near the tail pipe may result in a fire starting.
Various approaches are known for addressing the issues associated with overloading of particulate filters. In one example approach, DE 102 06 805 A1 describes a soot filter for the purification of exhaust gases which has a predetermined breaking point for reducing an exhaust-gas counter-pressure. The predetermined breaking point may be arranged in a filter body of the filter and/or in a bypass line of the filter. However, the inventors herein have recognized that such an approach compromises the functionality of the filter in order to reduce the exhaust-gas counter-pressure. As such, the breaking point approach may result in undesirable exhaust emissions, among other disadvantages.
To address the above issues, the inventors herein have identified a particulate filter and associated methods addressing the issue of particulate filter overloading without compromising the filter's ability to retain exhaust particles. Further, the inventors herein have identified example methods for mitigating dangers associated with engine shutdown during regeneration of a particulate filter.
In one example, a particulate filter for a vehicle exhaust system comprises a primary filter, a secondary filter, and a quenching agent injection nozzle arranged upstream of the primary filter. An exhaust-gas path runs through the primary filter in a normal mode and through the secondary filter in a fail-safe mode. In the fail-safe mode, the quenching agent injection nozzle delivers quenching agent to the primary filter. By delivering quenching agent to the primary filter in the fail-safe mode, exothermic heat generated during the sudden combustion of stored soot particles may be limited by means of the quenching agent, thereby reducing damage to the exhaust system. Further, because the exhaust-gas path runs through the secondary filter when the primary filter is overloaded, the exhaust gas continues to be filtered even during primary filter overload. In this way, emissions regulations may still be adhered to and damage to the exhaust system may be prevented despite overloading of the primary filter.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.